refactor: remove LocaleSwitcher component and update locale handling

- Removed LocaleSwitcher from NavUser, SiteHeader, and WorkbenchHeader components.
- Updated tests to reflect the removal of LocaleSwitcher.
- Changed default locale from "en-US" to "zh-CN" in i18n configuration.
- Refactored locale resolution logic to read configured locale without relying on browser language detection.
- Updated AgentDesk SDK to support language configuration from public API.
- Cleaned up unused auth options fetching in the auth API.

web/components/nav-user.tsx

@@ -6,7 +6,6 @@ import { useState } from "react"
 import { useAuth } from "@/components/auth-provider"
 import { useI18n } from "@/i18n/provider"
 import { ChangePasswordDialog } from "@/components/change-password-dialog"
-import { LocaleSwitcher } from "@/components/locale-switcher"
 import { useNotifications } from "@/components/notification-provider"
 import { PaletteToggle } from "@/components/palette-toggle"
 import { ThemeToggle } from "@/components/theme-toggle"
@@ -104,7 +103,6 @@ export function NavUser({
                   {t("nav.preferences")}
                 </DropdownMenuLabel>
                 <div className="flex items-center gap-2 px-2 pb-2">
-                  <LocaleSwitcher />
                   <PaletteToggle />
                   <ThemeToggle />
                 </div>